1. Field of the Invention
The present invention relates to methods for removing undesirable substances from tooth surfaces during dental procedures. The invention removes buildup of debris and bacteria formed during preparation of tooth surfaces during procedures such as root canal treatment, restoration, dental reconstruction, periodontal procedures, and the like, and is also suitable for preparation of bone for reconstruction or restoration.
2. Brief Description of the Related Art
As a consequence of pathological changes in the dental pulp, the root canal system acquires the capacity to harbor several species of bacteria, their toxins and their by-products. The microorganisms present in infected root canals are predominantly gram-negative anaerobes that are seeded into the root canals from direct pulp exposures (caries or traumatic injuries) or coronal microleakage. The morphology of root canals is very complex and mechanically prepared root canals contain areas that cannot be reached by endodontic instruments. The microorganisms present in the root canal not only invade the anatomic irregularities of the root canal system, but also invade the dentinal tubules.
In the root, dentinal tubules extend from the intermediate dentin just inside the cementum-dentin junction to the pulp-predentin junction. Tubules are approximately 1 μm in diameter near the cementum-dentin junction and approximately 2.5 μm near the pulp-predentin junction. The number of dentinal tubules per square millimeter varies from 8,000 to 57,000. At the periphery of the root at the cemento-enamel junction, the number has been estimated to be approximately 15,000 per square millimeter.
Many studies have shown that currently used methods of cleaning and shaping produce a smear layer that covers root canal walls. The smear layer is produced as a result of instrumentation and its content is forced into the dentinal tubules to varying distances. Moodnik, R. M., Dorn, S. O., Feldman, M. J., Levey, M., and Borden, B. G., J. Endodon., 1976, 2, 261-266; Cengiz, T., Aktener, B. O., and Piskin, B., Int'l. Endodon. J., 1990, 23, 163-171. Cengiz, et al. suggested that the penetration of smear material into the dentinal tubules is probably caused by capillary action generated between the dentinal tubules and the smear material.
In 1975, McComb and Smith described the smear layer in endodontics. McComb, D., and Smith, D. C., J. Endodon., 1975, 1, 238-242. It was later characterized as consisting of a superficial layer on the surface of the canal wall that averages between 1-2 μm in thickness, and a deeper layer packed into the dentinal tubules to a depth of up to 40 μm. Cameron, J. A., J. Endodon., 1983, 9, 289-292; Mader, C. L., Baumgartner, J. C., and Peters, D. D., J. Endodon., 1984, 10, 477-483. The smear layer consists of organic and inorganic substances that include fragments of odontoblastic processes, microorganisms and necrotic materials. A number of studies have shown that presence of smear layer can prevent penetration of root canal medications and sealers into the dental tubules. In addition, they have shown that removal of the smear layer results in better adaptation between root canal filling materials and the dentinal walls.
Bacteria present in the infected root canals usually invade the dentinal tubules and can re-infect the root canals if they remain viable after root canal therapy. Viable bacteria has been reported in dentinal tubules of infected teeth at approximately half the distance between the root canal walls and the cemento-dentinal junction. Endotoxins have been found within the dentinal walls of infected root canals as well. Concern has been evidenced regarding the fate of these bacteria, especially whether they may find nutrients for growth and reproduction.
Complete eradication of bacteria present in the canals and dentinal tubules, sealing root canals in three dimensions and prevention of recontamination of sealed root canals are the ideal goals for endodontic therapy. Because of the complexity of root canal systems, and the inability of instruments to contact all surfaces of the root canals, it is impossible to create a sterile space in all teeth with infected root canals. Bystrom, A., and Sundqvist, G., Scand, J. Dent. Res., 1981, 89, 321-328; Bystrom, A., Claesson, R., and Sundqvist, G., Endod. Dent. Traumatol., 1985, 1, 170-175. In fact, residual bacteria in an instrumented and unfilled canal can multiply to their original numbers within 2-4 days. To prevent repopulation of the root canals with residual bacteria, the use of intracanal medications and completion of treatment of infected root canals in more than one visit has been recommended. Bystrom, A., Claesson, R., and Sundqvist, G., Endod. Dent. Traumatol., 1985, 1, 170-175; Chong, B. S., and Pitt Ford, T. R., Int'l. Endodon. J., 1992, 25, 97-106.
Intracanal medications have traditionally been considered important to success of root canal therapy. In fact, it has been a common assumption that success, both short- and long-term, depends on the chemicals placed in the canal between appointments. However, there is no firm scientific evidence for usefulness of medications such as camphorated monochlorophenol (CMCP), formocresol, cresatin, or calcium hydroxide (Ca(OH)2), which have been used as intracanal medications. The intracanal medicaments have been proposed for, inter alia, antimicrobial use in the pulp and periapex, neutralization of canal remnants to render them inert, and control or prevention of post-treatment pain.
A study of the presence and influence of bacteria on the long-term success of root canal therapy showed that about 40% of root canals are infected after instrumentation. Sjogren, U., Figdor, D., Persson, S., and Sundqvist, G., Int'l; Endodon. J., 1997, 30, 297-306. In addition, instrumented canals without application of an intracanal medication with Ca(OH)2 failed significantly more frequently than those which were medicated for one week with Ca(OH)2 (68% vs. 94%). The results of this study corroborate a 1987 study showing improved clinical success rates following effective disinfection of root canals. Bystrom, A., Happonen, R., Sjogren, U., and Sundqvist, G., Endod. Dent. Traumatol., 1987, 3, 58-63.
According to a number of authorities, presence of smear layer can inhibit penetration of anti-microbial agents such as intra-canal irrigants and medicaments into the dentinal tubules. Haapasalo, M., and rstavik, D., J. Dent. Res., 1987, 66, 1375-1379; Czonstkowsky, M., Wilson, E., and Holstein, F., Dental Clinics of N. Am., 1990, 34, 13-24. Several investigators have reported better adhesion of obturation materials to the canal walls after removal of the smear layer. Goldberg, F., and Abramovich, A., J. Endodon., 1977, 3, 101-105; White, R. R., Goldman, M., and Lin, P. S., J. Endodon., 1984, 10, 558-562. Several studies have also reported poor or no penetration of sealer in tubules with an intact smear layer. These studies have shown improved penetration following removal of the smear layer with sealers such as Tubliseal (penetration to 15 μm); AH26 (penetration from 10-60 μm); and Sealpex, Roth's 811, and CRCS (all with penetration from 35-80 μm). Gutierrez, J. H., Herrera, V. R., Berg, E. H., Villena, F., and Jofre, A., Oral Surg. Oral Med. Oral Path., 1990. 70, 96-108; Pallares, A., and Faus, V., Int'l. Endodon. J., 1995, 28, 266-269; Kouvas, V., Liolios, E., Vassiliadis, L., Parissis-Messismeris, S., and Boutsioukis, A., Endod. Dent. Traumatol., 1998, 14, 191-195.
Additionally, the presence or absence of the smear layer is believed to play an important role in the adhesive strength of a sealer to the dentinal walls. One study found a significant increase in adhesive strength of AH26 sealer when the smear layer was removed. Gettleman, B. H., Messer, H. H., and ElDeeb, M. E., J. Endodon., 1991, 17, 15-20. These findings correlate with the results of another study demonstrating an increase in resistance to microleakage of AH26 when the smear layer was removed. Economides, N., Liolios, E., Kolokuris, I., and Beltes, P., J. Endodon., 1999, 25, 123-125.
Contrary to these findings, some studies have found that the presence or absence of the smear layer has no significant effect on apical leakage. Evans, J. T. and Simon, J. H. S., J. Endodon., 1986, 12, 101-107. Kennedy, W. A., Walker, W. A., and Gough, R. W., J. Endodon., 1986, 12, 21-27; Economides, N., Liolios, E., Kolokuris, I., and Beltes, P., J. Endodon., 1999, 25, 123-125; Timpawat, S., and Sripanaratanakul, S., J. Endodon., 1998, 24, 343-345.
It has been shown that removal of smear layer before sealing of the root canal system allows better adaptation between the obturation materials and the root canal walls. Yamada, R. S., Armas, A., Goldman, M., and Lin, P. S., J. Endodon., 1983, 9, 137-142; Czonstkowsky, M., Wilson, E., and Holstein, F., Dental Clinics of N. Am., 1990, 34, 13-24. One study examined the adaptation of a mechanically softened gutta percha to the dentinal walls and reported that removal of the smear layer resulted in entry of gutta percha into the dentinal tubules. Pallares, A., and Faus, V., Int'l. Endodon. J., 1995, 28, 266-269. These authors reported no gutta percha penetration into the dentinal tubules in canals with intact smear layer. Another study reported that when Thermafil, Ultrafill and cold lateral condensation techniques were used as obturation methods, all techniques showed significant resistance to microleakage with the smear layer removed. Gencoglu, N., Samani, S., and Gunday, M., J. Endodon., 1993, 19, 558-562. Vertical condensation of gutta percha, Thermafil, and lateral compaction techniques with Ultrafill have also been reported to reduce microleakage with the smear layer removed. Taylor, J. K., Jeansonne, B. G., and Lemon, R. R., J. Endodon., 1997, 23, 508-512; Karagoz-Kucukay, I., and Bayirli, G., Int'l. Endod. J., 1994, 27, 87-93. In contrast to these findings, some studies have reported that removal of smear layer had no significant effect on microleakage of canals filled with laterally condensed gutta percha or Thermafil and System B (warm vertical) obturation techniques. Saunders, W. P., and Saunders, E. M., J. Endodon., 1994, 20, 155-158; Kytridou, V., Gutmann, J. L., and Nunn, M. H., Int'l. Endodon. J., 1999, 32, 464-474. Even if the smear layer cannot be fully removed, one of skill in the art will recognize that it is desirable to remove as much of the smear layer as possible, while sterilizing the portion that remains, prior to proceeding with filling, reconstruction, restoration, or final treatment.
The components of the smear layer are very small particles with a large surface/mass ratio, which makes them very soluble in acids. Because of this characteristic, certain acids have been used in an attempt to remove the smear layer. Different formulations of ethylenediamine tetraacetic acid (EDTA) have been used to remove the smear layer from the surface of instrumented root canals, including REDTA (Roth EDTA). McComb, D., and Smith, D. C., J. Endodon., 1975, 1, 238-242. Some investigators, however, have questioned the effectiveness of REDTA by showing that when used alone, REDTA removes the inorganic portion of the smear layer but leaves an organic layer intact in the tubules. Goldman, M., Goldman, L. B., Cavaleri, R., Bogis, J., and Lin, P. S., J. Endodon., 1982, 8, 487-492. Sodium hypochlorite (NaOCl) has been shown to be very effective against this organic layer. When used alone, NaOCl can dissolve pulpal remnants, as well as predentin, but is ineffective in removing the smear layer. The alternating use of EDTA and NaOCl, however, has been reported to be an effective method to remove the smear layer. Goldman, M., Goldman, L. B., Cavaleri, R., Bogis, J., and Lin, P. S., J. Endodon., 1982, 8, 487-492; Yamada, R. S., Armas, A., Goldman, M., and Lin, P. S., J. Endodon., 1983, 9, 137-142; Baumgartner, J. C., and Mader, C. L., J. Endodon., 1987, 13, 147-157. One study recommends the use of NaOCl during instrumentation, along with an EDTA rinse followed by a final flush with NaOCl. Baumgartner, J. C., and Mader, C. L., J. Endodon., 1987, 13, 147-157. Another study compared the ability of various salts of EDTA to remove the smear layer and concluded that all salts of EDTA were capable of removing the smear layer from the coronal two thirds of root canals. In addition, the same study reported that tetrasodium salt, pH adjusted with HCl, is less expensive and just as effective as the more commonly used disodium EDTA. O'Connell, M. S., Morgan, L. A., Beeler, W. J., and Baumgartner, J. C., J. Endodon., 2000, 26, 739-743.
In 1993, a solution of EDTA and ethylenediamine was developed to work in a dual action. Aktener, B. O., and Bilkay, U., J. Endodon., 1993, 19, 228-231. The goal was to see if a single irrigating solution can be developed to remove the inorganic as well as the organic components of the smear. Many patent tubules were found, but more research was deemed necessary to determine the efficacy of this combination. Other studies have added a quaternary ammonium bromide to EDTA to reduce its surface tension. Goldberg, F., and Abramovich, A., J. Endodon., 1977, 3, 101-105; Ciucchi, B., Khettabi, M., and Holz, J., Intl. Endod. J., 1989, 22, 21-28. This addition increased the wetting effect on the canal wall and permitted deeper penetration of the solution into irregularities. EDTAC, as it is named, was shown to be very effective in smear layer removal, reaching its peak effect at 15 minutes and increasing the diameter of the opened dentinal tubules. Goldberg, F., and Spielberg, C., Oral. Surg., 1982, 53, 74-77. Another study reported effective removal of the smear layer when using a solution of EDTA, carbamide peroxide, and propylene glycol. Tam, A., and Yu, D. C., Compendium Cont. Ed. Dent., 2000, 21, 967-972. Recently, ethylene glycol-bis(b-aminoethyl ether-NNNN-tetraacetic acid), EGTA, was reported to be somewhat effective in removing the smear layer without inducing erosion commonly caused by EDTA. Calt, S., and Serper, A., J. Endodon., 2000, 26, 459-461.
The quantity of smear layer removed by an acid is directly related to the concentration of the acid (pH) and the time of exposure. Morgan, L. A., and Baumgartner, J. C., Oral Surg. Oral Med. Oral Path., 1997, 84, 74-78. Several studies used a 50% citric acid solution to treat canal walls after instrumentation and found better penetration of rosin sealer into the walls and improved adaptation of gutta percha when compared to untreated canals. Loel, D., J. A. D. A., 1975, 90, 148-151; Tidmarsh, B., J. Endodon., 1978, 4, 117-121; Baumgartner, J. C., Brown, C. M., Mader, C. L., Peters, D. D., and Shulman, J. D., J. Endodon., 1984, 10, 525-531. When citric acid was used as the sole agent for removal of smear layer, solutions at concentrations below 50% were ineffective. Yamada, R. S., Armas, A., Goldman, M., and Lin, P. S., J. Endodon., 1983, 9, 137-142; Takeda, F. H., Harashima, T., Kimura, Y., and Matsumoto, K., Intl. Endodon. J., 1999, 32, 32-39. Lactic acid at 50% concentration is less effective than 50% citric acid for removal of smear layer. Wayman, B. E., Kopp, W. M., Pinero, G. J., and Lazzari, E. P., J. Endodon., 1979, 5, 258-265. This could possibly be attributed to the viscosity of lactic acid. Additionally, alternating use of 10% citric acid and 2.5% NaOCl has also been reported to be a very effective method for removing the smear layer. Wayman, B. E., Kopp, W. M., Pinero, G. J., and Lazzari, E. P., J. Endodon., 1979, 5, 258-265.
In 1989, one study reported that 25% tannic acid was effective in removing the smear layer, but another study refuted these findings and explained that tannic acid increased the cross-linking of exposed collagen within the smear layer and within the matrix of the underlying dentin, thus increasing organic cohesion to the tubules. Bitter, N. C., Oral Surg. Oral Med. Oral Path., 1989, 67, 333-337; Sabbak, S. A., and Hassanin, M. B., J. Prosthet. Dent., 1998, 79, 169-174.
Polyacrylic acid (Durelon liquid and Fuji II liquid) at 40% has been reported to be very effective for removal of smear layer. Berry, B. A., von der Lehr, W. N., and Herrin, B. K., J. A. D. A., 1987, 115, 65-67. Because of its potency, however, it is recommended that application of Polyacrylic acid should not exceed 30 seconds.
Derivatives of oxine (8-hydroxy-quinoline) have been known to possess antiseptic qualities as early as 1895. Dequalinium compounds, which belong to this group, have been widely used in medicine against infections of bacteria, molds and fungi. Bis-dequalinium-acetate (BDA) has been shown to remove the smear layer throughout the canal, even in the apical third. Kaufman, A. Y., Binderman, I., Tal, M., Gedalia, I., and Peretz, G., Oral Surg., 1978, 46, 283-295; Kaufman, A. Y., Oral Surg., 1981, 51, 434-441. BDA is well tolerated by the tissues within the periodontium and has a low surface tension that allows penetration into spaces that instruments cannot reach. BDA is also considered less toxic than NaOCl and can be used interoperatively as a root canal dressing. One study compared Salvizol (a commercial brand of 0.5% BDA) with 5.25% NaOCl and found both comparable in their ability to remove organic debris, but only Salvizol was able to open dentinal tubules. Kaufman, A. Y., and Greenberg, I., Oral Surg., 1986, 62, 191-196. Another study reported Salvizol to be less effective at opening dentinal tubules compared to REDTA. Berg, M. S., Jacobsen, E. L., BeGole, E. A., and Remeikis, N. A., J. Endodon., 1986, 12, 192-197.
The effects of the tetracycline family of antibiotics on removal of smear layer have also been studied to a degree. These materials have been used to demineralize dentin surfaces, uncover and widen the orifices of dentinal tubules and expose the dentin collagen matrix. These effects provide a matrix that stimulates fibroblast attachment and growth. Studies have shown that doxycyline HCl (100 mg/ml) is an effective material to remove the smear layer from the surfaces of instrumented canals and those prepared for root-end filling materials. Barkhordar, R. A., Watanbe, L. G., Marshall, G. W., and Hussain, M. Z., Oral Surg. Oral Med. Oral Path., 1997, 84, 420-423; Barkhordar, R. A., and Russel, T., Cal. Dent. Assn. J., 1998, 26, 841-844; Haznedaroglu, F. and Ersev, H., J. Endodon., 2001, 27, 738-740. These studies speculate that a reservoir of active antibacterial agent might be created since doxycycline readily attaches to dentin and can be readily released later. Another study has reported increased demineralization effect when a 5% tetracycline/33% citric acid gel was used to treat teeth with moderate periodontal disease. Jeong, S., Han, S., Lee, S., and Magnusson, I., J. Periodontol., 1994, 65, 840-847.
Apart from chemical solutions, mechanical methods, including ultrasonic instrumentation, have been widely reported to be effective in removing the smear layer from prepared tooth surfaces. Laser removal of the smear layer has been shown to be successful as well for vaporizing tissues in the main canal, removing the smear layer, and eliminating residual tissue in the apical portion of root canals. Since laser beams travel in straight lines, however, the use of lasers in curved canals is limited.
Smear layers are also formed when tooth material is removed preparatory to restoration or other dental work, as it is for root canal situations. Moreover, in the restoration of bone, such as in orthopaedic restorations, debris layers similar in many respects to endodontic smear layers are also formed. It is now believed that their removal would be highly desirable as well.
Accordingly, it is believed to be highly desirable to remove the smear layer from a prepared root canal space prior to filling the canal. However, removal of smear layer materials is very difficult to accomplish. Moreover, there are no present methods likely to effect substantially complete removal of smear layers. Prior attempts have used a number of chemical species to remove the smear layer and sterilize the root surface(s), but with indifferent results. The removal of smear layer materials with a unitary solution to yield effective, convenient, and rapid smear layer removal is desired. All of this must be accomplished without interfering with the essential purpose of root canal preparation or with the eventual restoration of the space. Removal of smear layers from tooth restoration sites, periodontal loci, and other prepared locations for dental and periodontic work is a further object. Indeed, it is also believed to be desirable to remove smear layers from orthopaedic and bone restoration sites within or without the oral cavity as well.